Extensive research has been reported on the efficiency of nanomaterials for the targeted delivery of anticancer drugs. This paper exploited density functional theory (DFT) to assess the drug carrier performance of bare and X-doped ZnO nanotubes (X = In, Al, and Ge) toward the thioguanine (TG) anticancer drug. Bare ZnO nanotubes were found to be inefficient for the delivery of TG molecules. The In, Al, and Ge dopants, however, increased the adsorption energy of the ZnO nanotubes from −7.8 to –33.6, −28.5, and −30.8 kcal/mol, respectively. The natural bond orbital (NBO) analysis revealed that the charge transfer was remarkable from the adsorbate to the doped adsorbents. The solvent effects on the adsorption energy were studied in an aqueous medium. The adsorption energy of the In-doped ZnO nanotubes declined from –33.6 to −21.4 kcal/mol. It was concluded that X-doped ZnO nanotubes are promising carriers of TG drug molecules.